The present invention relates generally to bandwidth control for digital data transmission. More particularly, the present invention relates to network congestion recognition and management.
Multimedia communications channels such as those used in Internet videoconferencing generally employ the user datagram protocol (UDP) to transport packets of video data. Because UDP does not support the retransmission of lost packets, it is well-suited to real-time data transmission. The delay required for the retransmission of a lost packet in a real-time multimedia communications channel would produce a noticeable fault at the receiver such as frozen video and clicks in the audio.
However, UDP is a connectionless protocol, and so presents a network security issue. Many businesses will not permit UDP connections to traverse their corporate firewalls, and so cannot use UDP videoconferencing systems.
However, another transport protocol is available, namely transmission control protocol (TCP). But TCP retransmits lost packets, and so is generally not well-suited for real-time multimedia communications. TCP also provides network congestion control by effectively changing the bandwidth of the communications channel, lowering the bandwidth of each channel on a congested network connection to allow all of the channels to share the network connection. This congestion control can adversely affect multimedia communications. For example, if a videoconferencing application is transmitting at a bandwidth greater than that permitted by TCP congestion control, a growing transmission lag will result. If the difference in bandwidths is 10%, then at the end of a one-hour videoconference the lag will be 6 minutes, hardly real-time.